Why Is This So True Meaning?

So, "So true!" means "I agree with you 100%." The context is: I was reading some comments on yahoo about a news article. One of the comments said, "The comments are more interesting than the news article." My response was "So true!"

How do you say it is so true?

Synonyms for it's true in English yes indeed; definitely; actually; certainly; truly; really; verily; in truth; real; actual; to be sure; it's true; genuine; indeed.

How do you use so true?

The Squid And The Whale may sound downbeat and depressing, but it is so true to life, it turns out funny and compassionate. Its hard to trust when your feelings are so naked, so raw, so harsh, so true.